The present disclosure relates generally to polymer extrusion systems, and more particularly, to polymer extrusion systems of polyolefin manufacturing systems.
This section is intended to introduce the reader to aspects of art that may be related to aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
As chemical and petrochemical technologies have advanced, the products of these technologies have become increasingly prevalent in society. In particular, as techniques for bonding simple molecular building blocks into longer chains or polymers have advanced, the polymer products, typically in the form of various plastics, have been increasingly incorporated into various everyday items. For example, polyolefin polymers, such as polyethylene, polypropylene, and their copolymers, are used for retail and pharmaceutical packaging, food and beverage packaging, household containers, household items, automobile components, pipes, conduits, and various industrial products.
Specific types of polyolefins, such as high-density polyethylene (HDPE), have particular applications in the manufacture of extruded, blow-molded, and injection-molded goods, such as food and beverage containers, film, and plastic pipe. Other types of polyolefins, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), isotactic polypropylene (iPP), and syndiotactic polypropylene (sPP) are also suited for similar applications. The mechanical requirements of the application (e.g., tensile strength, impact strength, modulus, and hardness), the physical requirements (e.g., thermal stability, molecular weight, and density), and the phase behavior (e.g., glass transition temperature, melt and melt crystallization temperatures) typically determine what type of polyolefin is suitable.
One benefit of polyolefin construction, as may be deduced from the list of uses above, is that it is generally non-reactive with goods or products with which it is in contact. This allows polyolefin products to be used in residential, commercial, and industrial contexts, including food and beverage storage and transportation, consumer electronics, agriculture, shipping, and vehicular construction. The wide variety of residential, commercial, and industrial uses for polyolefins has translated into a substantial demand for raw polyolefin which can be extruded, injected, blown, or otherwise formed into a final consumable product or component.
To satisfy this demand, various processes exist by which olefins may be polymerized to form polyolefins. Typically, these processes are performed at or near petrochemical facilities, which have ready access to the short-chain olefin molecules (monomers and comonomers), such as ethylene, propylene, butene, pentene, hexene, octene, decene, and other building blocks, of the much longer polyolefin polymers. These monomers and comonomers may be polymerized in a liquid-phase polymerization reactor and/or gas-phase polymerization reactor to form a product including polymer (polyolefin) solid particulates, typically called fluff or granules. The fluff may possess one or more melt, physical, rheological, and/or mechanical properties of interest, such as density, melt index (MI), melt flow rate (MFR), copolymer content, comonomer content, modulus, and crystallinity. The reaction conditions within the reactor, such as temperature, pressure, chemical concentrations, residence time, polymer production rate, and so forth, may be selected to achieve the desired fluff properties.
The fluff from the reactors may be mixed with additives and/or further processed before being used to produce the goods and products listed above. For example, the fluff may be extruded in an extruder and passed through a pelletizer to form polymer pellets, which may be easier to handle and transport to manufacturers of plastic goods than fluff. High pressures may be used in the extruder and pelletizer to convert the fluff into pellets. It is now recognized that undesirable issues may arise when the pressure within the extruder varies excessively and/or exceeds certain thresholds. For example, certain equipment associated with the extruder may be shut down when a high-pressure threshold is exceeded, thereby interrupting pellet production and/or causing reactor production rates to be reduced. Such unwanted production upsets may reduce the efficiency of the polyolefin manufacturing system, increase expenses associated with production of the pellets, increase maintenance costs, and/or contribute to poor equipment reliability.